There are many circumstances in which a signal's frequency must be multiplied. For instance, a clock signal's frequency is often multiplied numerous times within a computer system to accommodate the clocking requirements of the various components with the system (e.g., microprocessors, audio components, IR interfaces, etc.). Each required clock signal for each component is supplied from a common, relatively low frequency clock signal that is multiplied to the desired frequency.
In addition to supplying multiple clock signals, frequency multipliers typically are employed within microprocessors having operating frequencies above about 200 MHZ. Because a 200 MHZ or faster clock signal broadcasts if transmitted over a wire, a 50 MHZ external clock typically is employed to drive a high speed microprocessor. A frequency multiplier within the microprocessor multiplies the 50 MHZ clock signal to the required high frequency (e.g., 200-400 MHZ) and thus avoids broadcasting issues.
Digital frequency multipliers (DFMs) which digitally multiply signal frequency are known in the art. Conventional DFMs typically include a ring oscillator for generating the multiplied frequency from a reference frequency and a plurality of dividers that provide the required multiplication factor.
While capable of multiplying signal frequency, most conventional DFMs suffer from several drawbacks. For instance, DFMs typically tune a ring oscillator to the desired multiplied frequency and then "lock" the ring oscillator's oscillation frequency so as to prevent further adjustments to the oscillation frequency. Once locked, the DFM cannot compensate for drift (e.g., thermally induced) in the ring oscillator's oscillation frequency, and an erroneous multiplied frequency may result. Further, conventional DFMs are not easily testable, especially during operation, and generally are not readily scalable because the repowering circuitry required to drive additional logic gates within a conventional DFM affects the internal delays of the DFM's ring oscillator and thus the multiplicative properties of the DFM.
Accordingly, a need exists for a DFM that adjusts ring oscillator oscillation frequency even after the desired oscillation frequency is reached, that can be tested during operation and that is easily scalable.